Field of Endeavor
The present invention relates to non-contact registration of pressure, sound and ultrasound waves and more particularly to a non-contact, all optical system for detecting ultrasound or other types of pressure waves.
State of Technology
Ultrasound is widely used in various applications such as in the medical field and for the detection of defects in solid-state material or components. Typically, the ultrasound waves are injected in to the material and the reflected signal from an object (such as a crack in a homogeneous material or a cyst or tumor in a tissue or organ system) is detected and/or imaged using an appropriate ultrasound detector system. Typically, an impedance matching material is used to effectively couple the ultrasound wave energy from the emitter to the material and the reflected signal from the material to the detector for minimizing loss of signal.
The ultrasound signal to be detected can also be generated via other means. In this case, the object of interest becomes the primary emitter of the ultrasound signal. One such example is associated by the absorption of another form of energy by a defect or defective region which in turn leads to localized energy deposition followed by heating, spatial expansion and subsequently the emission of a pressure wave by this defect. When this process is modulated at ultrasound frequencies, the repeated production of pressure waves leads to the generation of the ultrasound waves that originate in the defect location.
Another method suitable for biomedical applications is associated with the injection of light pulses that is absorbed by structures of interest such as cysts, tumors and normal or abnormal blood concentrations. The resulting pressure waves following the absorption of light energy can then be used to achieve detection or imaging of the tissue structure of interest. Contrary to the highly diffusive way the light propagates in tissues, ultrasound waves exhibit comparatively very limited attenuation and thus, is capable for transporting the signal information through greater distances inside the tissue.
Ultrasound waves are typically strongly reflected by a surface or object that presents impedance mismatching (such as the skin-air interface or at the surface of a solid state material). For this reason, an impedance matching fluid is typically used to achieve best coupling of the ultrasound wave energy to the detection system. This limits the use of ultrasound methods to detection schemes that require the detector to be in contact with the system under examination (such as the tissue).
The present invention provides a medium that when applied on the surface of an object, such as tissue, allows for remote detection and registration of the ultrasound waves reaching the surface using light-based methods. The method is also suitable for detecting of pressure waves outside the ultrasound frequency range, thus it can be used to detect sound waves or any type of pressure waves that can be transmitted through the tissue or other material of interest.